A fixing device for use in an electrophotographic image forming apparatus is known in the art, in which a fusing film is nipped between a backup member (e.g., pressure roller) and a nip plate as a heating plate heated by a heater to thereby form a nip portion between the backup member and fusing film interposed between the backup member and the nip plate, and a holding member (e.g., stay) is provided to hold the heater and the nip plate. One example of the nip plate is a bent plate shaped like a letter U in cross section, such that sidewall portions of the U-shaped nip plate are fitted in stepped portions formed on insides of wall portions of a U-shaped stay (holding member). Thus, end faces of the sidewall portions of the nip plate are in contact with surfaces opposite thereto of the stepped portions of the stay so that a pressing force applied to the nip plate by a pressure roller (backup member) is transmitted through the end faces of the sidewall portions of the nip plate and received by the stay.
In the fixing device as mentioned above, however, the nip plate is supported with its very small areas of the end faces abutted on the stay, and the end faces of sidewall portions of the nip plate would possibly become slipped off the stepped portions of the stay. It would thus be desirable to provide a fixing device in which the nip plate is supported on the stay in a more reliable manner.